Weight of the Patient

The optimum therapeutic dose intended to produce a specific effect in an individual is generally determined in terms of the amount of drug per kilogram of body weight of that person (1 kg = 2.2 lbs). However, it must be kept in mind that drug dosages may have to be altered in the presence of such factors as age (Figure 1), obesity, and various disease states such as liver and kidney disease that affect pharmacodynamic and pharmacokinetic processes.

Figure 1. Age-related pharmacokinetic variables.

In general, if the manufacturer’s maximum recommended dose (MRD) of a drug for a healthy adult per day is 60 mg/kg/day to be administered in three equal doses and the patient weighs 143 lbs (i.e., 65 kg), then the daily MRD for that individual is 3900 mg (60 mg/kg/day x 65 kg) to be administered in 1300 mg doses three times a day. It is of note that if a person weighs more than 165 lbs (i.e., ≥75 kg), the MRD should only be exceeded with extreme caution.